<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

<!--hr标签，就是横线标签，画一条横线出来-->

<hr>

<!-- %就是占父级元素的多少比例 -->
<hr width="50%">

<hr width="50%" align="left">

<hr width="100" align="left">

</body>
</html>